Effects of carbon concentration and filament number on advanced internal Mg infiltration-processed MgB2 strands

In this paper we show that an advanced internal Mg infiltration method (AIMI) is effective in producing superconducting wires containing dense MgB2 layers with high critical current densities. The in-field critical current densities of a series of AIMI-fabricated MgB2 strands were investigated in terms of C doping levels, heat treatment (HT) time and filament numbers. The highest layer J(c) for our monofilamentary AIMI strands was 1.5 x 10(5) A cm(-2) at 10 T, 4.2 K, when the C concentration was 3 mol% and the strand was heat-treated at 675 degrees C for 4 h. Transport critical currents were also measured at 4.2 K on short samples and 1 m segments of 18-filament C doped AIMI strands. The layer J(c)s reached 4.3 x 10(5) A cm(-2) at 5 T and 7.1 x 10(4) A cm(-2) at 10 T, twice as high as those of the best powder-in-tube strands. The analysis of these results indicates that the AIMI strands, possessing both high layer J(c)s and engineering J(e)s after further optimization, have strong potential for commercial applications.